Have had a good 10 days of sailing, the first 5 days were 20+ mph. The next 2 were calm, stayed on the deck,last two were light winds of 5-10. I went out yesterday as we had a wee bit of a sea breeze, & coasted along at 5-10 mph max for a few hours. Of course it died finally, & I had the "nap on the tramp" as I drifted the last 1/2 mile.
Today, we had decent 10-13mph breeze, with a few gusts,so we rigged up & took the whole family for a an hour cruise. The old 5.7 still made pretty good time, even with 4 adults onboard.
About half way home I heard a bang, & saw the sail going quickly to leeward. My first thought was the mast was coming down. Luckily that proved not to be the case. The clew plate had blown completely apart, with a rain of rivets showering down on the tramp. It seems the heads all seperated, or sheared off.
Of course the multiple layers of sailcloth could not hold the hook, & it tore through, releasing the sail.
I undid the mast rotator line, & wove it into a bridle through through the remaining holes in the sail, so as to distribute the load, then placed the hook into the jerry rigged bridle.
This got us home, but better yet allowed us to pass the Albacore headed back to the same bay. Second place to an old Albacore would have been to painful to bear.
This was my spare (light wind sail, it's 10-12 sq ft larger than the original) & lightly used. The fabric is very crisp, the bolt rope shows almost no signs of wear, even the Skip Elliot decal shows almost no wear from folding etc.
It seems age & corrosion weakened the rivets to the point they failed under what I deemed a fairly light load. Upon inspection of the jib, I see two rivets missing the head.
My original 5.7 sail,(from a freshwater enviroment) despite seeing much more use, seems to have all rivets intact.
Luckily both sides of the clew plate landed on the tramp. I'm sending the piece containg rivet remains to a colleague in our fueselage structures shop for analysis of the rivets. I don't know enough about corrosion of aluminum to tell whether they failed due to load exceedance, or metal fatigue/corrosion.
I plan to get the guys who rivet skins in the fuselage dept to put it back together, using aviation rivets.
Can anyone tell me what, if anything needs to be done with the tear through the hole?
I'm thinking that it is the two plates fastened tightly together, gripping the material, that hold the load. The bit of fabric,(several layers thick) at the bottom of the hole doesn't do much?
Do the saltwater sailors see this sort of thing on a regular basis?
I have not operated Cats in salt water, & thought this sail would be as strong as new. Despite little previous use, it came from a salt water enviroment. I thought those rivets would not corrode, or is it more likely metal fatigue due to age?
I will certainly pay more attention to the head & clew plate fasteners from now on.





Edited by Edchris177 on Jul 19, 2011 - 03:42 AM.

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alloy corrodes and hardens in all environments

i seem to remember finding some dodgy looking heads on my 5.2 head? plate when i bought the boat

(nacra seem to have center-peened? mine which left a tiny, raised, easy to corrode ring)

so they got drilled and replacing with new solids and flattened with a sledge hammer as backplate and medium hammer as penner? aim to get the correct swell in 3-5 hits, too few hits and you risk bashing them flat/weak, too many hits and you risk hardening/weakening them, (former 747 sheet metal worker;o)

Murrays--19-2010 & 19-1510. I order them all the time (brass screws with nuts) to replace pocket protectors where rivits have corroded & fallen apart. Easier to put back together than rivits, but requires a small blade screwdriver. Pete

One of my better sails, one that came from a saltwater life, has a few of the rivets missing from the clew plate at the top as well.

Should I use aluminum or stainless rivets? I think the originals are brass...they look like it anyway.

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Rob
OKC
Pile of Nacra parts..
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I had something similar happen to my original (essentially homemade) sail. I replaced the clew plate using tiny stanless screws and nylock nuts. Worked great. I would think your rivets were corroded or not set properly.

Generally you are supposed to use the aluminum hammer set rivets but brass is MUCH stronger. I would go with pete's advice.

I've been reading up on sailmaking, tarpmaking (sewing myself some new wing seat tramps and making a custom cover for my boat) and i wouldn't discount the value of fabric reinforcing for distributing the load! I would bring the sail to your local loft and get them to sew in a reinforcing patch 2-3 layers thick with radial stitching to the clew plate. Then install the clew plate over top of that. Probably cost you less than 50 bucks and I doubt it will break again!

D.

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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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i would test all brass with a magnet to insure it contains no lead (often found in cheaper brass)

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(nacra seem to have center-peened? mine which left a tiny, raised, easy to corrode ring)

When I looked at the rivets, I thought that little ring would be the weak point, but that never failed, it was the heads that seperated.
I know what you mean about proper hammer technique, easy to pound to many times, & end up with shot peened hardening. I have access to people in Boeing structures, & also the Space shuttle program, one is a lead engineer on the Canada Arm. I was thinking holding it with cleekos(sp?). You can't really "draw" then rivet, I'm thinking clamp it tightly, then rivet. These people have pnumatic guns that fire the proper shots.
As an aside, were you a colleague of that chap who riveted the 747 tail pressure bulkhead that came apart. Poor bugger, felt so bad he ended it.

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(brass screws with nuts)

I know exactly what you mean Pete. I had my other sails gone over during the winter, & they replaced quite a few of the batten rivets with those. The batten plastic end pocket has little octogon depressions so the nuts fit flush. Would you use them on the clew plate though? They look rather large, especially when you put 30 odd of them in.

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Should I use aluminum or stainless rivets?

I don't think I would use stainless, the head/clew plate is aluminum. The dissimiliar metals is a known corrosion source on saltwater Cats.

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I would bring the sail to your local loft and get them to sew in a reinforcing patch 2-3 layers thick with radial stitching to the clew plate.

Dave, that area is already 4-5 layers thick, presumably for exactly the reason you stated.

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i would test all brass with a magnet to insure it contains no lead

Do you mean iron, Andrew? Lead is non ferrous, even 100% lead content will have no affinity for a magnet. I know what you mean concerning stainless steel, the cheaper stuff is magnetic, & corrodes much easier.

I think Erics comment about hardening in all enviroments, with the resultant brittleness is spot on. I'm going to send some of the rivets to the aerospace engineers, & see if they can shed some knowledge. I'll post what I find.
For all those with 20-30 year old sails, I would look at the plates closely. If any rivets are popped, change them out, now. This clew had none popped, & none seemed suspect with naked eye inspection. You can always jury rig something, but it would be a pain to have to come 20 miles home under 1/4 power. We were going to go 15 miles down the lake that day, glad we only went 5.

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One year at Ocean Springs I was about to launch the boat off the beach for the start of a race and when I went to connect the boom to the main the two halves of the clew plate dropped onto the ground just as described. All the rivets were dust.

I thought my sailing was over for the weekend but thanks to helpful fellow skippers who came to the rescue with a rivet gun the plate was popped back on and I was sailing again in no time.

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Damon Linkous
1992 Hobie 18
Memphis, TN

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Edchris177

As an aside, were you a colleague of that chap who riveted the 747 tail pressure bulkhead that came apart. Poor bugger, felt so bad he ended it.

ah, you mean the incorrectly done repair, (missed row of rivets), on the japan airlines 747 aft pressure bulkhead that blew out, leading to the single biggest? loss of life from a single aircraft crash?

not a colleague, but we were all made well aware of what went wrong and the need to stick EXACTLY to the plans as drawn up by the engineers in the offices...so far my forward pressure bulkhead work seems to be holding

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All the rivets were dust.

That's interesting. I had a quick conversation with a fellow in our metal shop today. He said they really couldn't give me any info, without looking at the rivets under magnification. I'm hoping to get some sample to them next week. If they can take some photos under magnification, I'll post them with what they tell me.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
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